Sodium-calcium exchange is a major mechanism of calcium homeostasis in many cell types. Physiological functions as diverse as vision, secretion and cardiac contractility are strongly dependent on sodium-calcium exchange activity. In the heart, exchanger function can become pivotal in pathological settings with possible outcomes of calcium overload, arrhythmias and ultimately death. In the last few years our understanding of sodium-calcium exchange has improved dramatically. Major successes have been achieved in the arenas of molecular biology, biophysics and cell biology. Structure-function studies of the cloned cardiac exchanger are well advanced. Multiple exchanger types are identified and characterized in different cell types (including brain, blood cells, smooth muscle and kidney). Molecular mechanisms of the exchange process and intrinsic exchanger 'gating' reactions are being elucidated. Multiple regulatory mechanisms are being characterized in different cell types. And the function of sodium-calcium exchange in a wide range of intact cells is being studied with improved electrical and optical methods. This symposium will highlight progress in each of these areas, giving special consideration to exchanger function in situations of medical/pathological interest.